Communication of high efficiency (he) long training fields (ltfs) in a wireless local area network (wlan)

ABSTRACT

A method performed by a STA may comprise transmitting an HE LTF of a data unit. The HE LTF may have a number of symbols based on a number of space-time streams utilized for the data unit. The HE LTF may be transmitted on a subset of subcarriers of a 20 MHz channel, a 40 MHz channel or an 80 MHz channel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/510,383, filed on Mar. 10, 2017, which is the National Stage Entryunder 35 U.S.C. § 371 Patent Cooperation Treaty Application No.PCT/US2015/049653, filed Sep. 11, 2015, which claims the benefit of U.S.Provisional Application No. 62/049,978, filed Sep. 12, 2014, thedisclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

Wireless networks (e.g., IEEE 802.1 lac based networks) may provideaccess points (APs) for one or more stations (STAs) in a basic serviceset (BSS) with one or more operating channels. The AP may have access orinterface to a distribution system (DS) or another type ofwired/wireless network that carries traffic in and out of the BSS.Traffic to STAs that originates from outside the BSS may arrive throughthe AP and be delivered to the STAs. Traffic originating from STAs todestinations outside the BSS may be sent to the AP to be delivered tothe respective destinations.

Traffic between STAs within the BSS may be sent through the AP where thesource STA sends traffic to the AP and the AP delivers the traffic tothe destination STA. Such traffic between STAs within a BSS may bepeer-to-peer traffic. Such peer-to-peer traffic may be sent directlybetween the source and destination STAs, e.g., with a direct link setup(DLS) using an 802.11e DLS or an 802.11z tunneled DLS (TDLS). A WLAN inIndependent BSS mode may have no AP and STAs communicate directly witheach other.

SUMMARY

A method performed by a STA may comprise transmitting a high efficiency(HE) long training field (LTF) of a data unit. The HE LTF may have anumber of symbols based on a number of space-time streams utilized forthe data unit. The HE LTF may be transmitted on a subset of subcarriersof a 20 megahertz (MHz) channel, a 40 MHz channel or an 80 MHz channel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. TA depicts an exemplary communications system.

FIG. 1B depicts an exemplary wireless transmit/receive unit (WTRU).

FIG. 1C depicts an exemplary wireless local area network (WLAN).

FIG. 2 depicts an example of three physical layer (PHY) protocol dataunit (PPDU) formats in 802.11n (High Throughput).

FIG. 3 depicts an example of a STG Short format.

FIG. 4 depicts an example of a SIG field with STG short format

FIG. 5 depicts an example of a STG Long format

FIG. 6 depicts an example of a SIG-A field in STG lone format. whensingle user transmission is utilized.

FIG. 7 depicts an example of a SIG-A field in STG lone format when multiuser transmission is utilized.

FIG. 8 depicts an example of an STG 1M format.

FIG. 9 depicts an example of a SIG field in STG 1M format.

FIG. 10 depicts an example of a VHT mixed format packet in 802.11ac.

FIG. 11 depicts an example of a Membership Status Array field.

FIG. 12 depicts an example of User Position Array field.

FIG. 13 depicts an example of a HEW PPDU design for simultaneoustransmissions.

FIG. 14 depicts an example of a HEW PPDU for UL MU-MIMO.

FIG. 15 depicts an example of a HEW PPDU for UL MU-MIMO.

FIG. 16 depicts an example of a hewSTF/hewLTF for UL MU-MIMO.

FIG. 17 depicts an example of another hewSTF/hewLTF for UL MU-MIMO.

FIG. 18 depicts an example of a hewSTF/hewLTF for UL MU-MIMO.

FIG. 19 depicts an example of a hewSTF/hewLTF for UL MU-MIMO.

FIG. 20 depicts an example of a PPDU design for coordinated orthogonalblock-based resource allocation, such as orthogonal frequency divisionmultiple access (OFDMA) transmissions with sub-channel size greater orequal to 20 MHz (e.g., a long OFDMA PPDU).

FIG. 21 depicts an example of a PPDU design for OFDMA transmissions withsub-channel size greater or equal to 20 MHz (e.g., a short OFDMA PPDU).

FIG. 22 depicts an example of procedures to select long/short OFDMA PPDUformat.

FIG. 23 depicts an example of a PPDU design for OFDMA transmissions withsub-channel size greater or equal to 20 MHz (e.g., a long OFDMA PPDU).

FIG. 24 depicts an example of a PPDU design for OFDMA transmissions withsub-channel size greater or equal to 20 MHz (e.g., a short OFDMA PPDU).

FIG. 25 depicts an example of a PPDU design for OFDMA transmissions withsub-channel size greater or equal to 20 MHz (e.g., a short OFDMA PPDU).

FIG. 26 depicts an example of a transmission design for hewSIG field.

FIG. 27 depicts an example of an uplink multi-user (MU) channel accessscheme.

DETAILED DESCRIPTION

A detailed description of illustrative embodiments is described withreference to the various figures. Although this description provides adetailed example of possible implementations, it should be noted thatthe details are intended to be exemplary and in no way limit the scopeof the application. In addition, the figures may illustrate one or moremessage charts, which are meant to be exemplary (the messages may bevaried, reordered, or even omitted where appropriate).

FIG. 1A is a diagram of an example communications system 100 in whichone or more disclosed features may be implemented. For example, awireless network (e.g., a wireless network comprising one or morecomponents of the communications system 100) may be configured such thatbearers that extend beyond the wireless network (e.g., beyond a walledgarden associated with the wireless network) may be assigned QoScharacteristics.

The communications system 100 may be a multiple access system thatprovides content, such as voice, data, video, messaging, broadcast,etc., to multiple wireless users. The communications system 100 mayenable multiple wireless users to access such content through thesharing of system resources, including wireless bandwidth. For example,the communications systems 100 may employ one or more channel accessmethods, such as code division multiple access (CDMA), time divisionmultiple access (TDMA), frequency division multiple access (FDMA),orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), and the like.

As shown in FIG. 1A, the communications system 100 may include at leastone wireless transmit/receive unit (WTRU), such as a plurality of WTRUs,for instance WTRUs 102 a, 102 b, 102 c, and 102 d, a radio accessnetwork (RAN) 104, a core network 106, a public switched telephonenetwork (PSTN) 108, the Internet 110, and other networks 112, though itshould be appreciated that the disclosed embodiments contemplate anynumber of WTRUs, base stations, networks, and/or network elements. Eachof the WTRUs 102 a, 102 b, 102 c, 102 d may be any type of deviceconfigured to operate and/or communicate in a wireless environment. Byway of example, the WTRUs 102 a, 102 b, 102 c, 102 d may be configuredto transmit and/or receive wireless signals and may include userequipment (UE), a mobile station, a fixed or mobile subscriber unit, apager, a cellular telephone, a personal digital assistant (PDA), asmartphone, a laptop, a netbook, a personal computer, a wireless sensor,consumer electronics, and the like.

The communications systems 100 may also include a base station 114 a anda base station 114 b. Each of the base stations 114 a, 114 b may be anytype of device configured to wirelessly interface with at least one ofthe WTRUs 102 a, 102 b, 102 c, 102 d to facilitate access to one or morecommunication networks, such as the core network 106, the Internet 110,and/or the networks 112. By way of example, the base stations 114 a, 114b may be a base transceiver station (BTS), a Node-B, an eNode B, a HomeNode B, a Home eNode B, a site controller, an access point (AP), awireless router, and the like. While the base stations 114 a, 114 b areeach depicted as a single element, it should be appreciated that thebase stations 114 a, 114 b may include any number of interconnected basestations and/or network elements.

The base station 114 a may be part of the RAN 104, which may alsoinclude other base stations and/or network elements (not shown), such asa base station controller (BSC), a radio network controller (RNC), relaynodes, etc. The base station 114 a and/or the base station 114 b may beconfigured to transmit and/or receive wireless signals within aparticular geographic region, which may be referred to as a cell (notshown). The cell may further be divided into cell sectors. For example,the cell associated with the base station 114 a may be divided intothree sectors. Thus, in one embodiment, the base station 114 a mayinclude three transceivers, i.e., one for each sector of the cell. Inanother embodiment, the base station 114 a may employ multiple-inputmultiple output (MIMO) technology and, therefore, may utilize multipletransceivers for each sector of the cell.

The base stations 114 a, 114 b may communicate with one or more of theWTRUs 102 a, 102 b, 102 c, 102 d over an air interface 116, which may beany suitable wireless communication link (e.g., radio frequency (RF),microwave, infrared (IR), ultraviolet (UV), visible light, etc.). Theair interface 116 may be established using any suitable radio accesstechnology (RAT).

More specifically, as noted above, the communications system 100 may bea multiple access system and may employ one or more channel accessschemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. Forexample, the base station 114 a in the RAN 104 and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Universal MobileTelecommunications System (UMTS) Terrestrial Radio Access (UTRA), whichmay establish the air interface 116 using wideband CDMA (WCDMA). WCDMAmay include communication protocols such as High-Speed Packet Access(HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed DownlinkPacket Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA).

In another embodiment, the base station 114 a and the WTRUs 102 a, 102b, 102 c may implement a radio technology such as Evolved UMTSTerrestrial Radio Access (E-UTRA), which may establish the air interface116 using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A).

In other embodiments, the base station 114 a and the WTRUs 102 a, 102 b,102 c may implement radio technologies such as IEEE 802.16 (i.e.,Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000,CDMA2000 1×, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), InterimStandard 95 (IS-95), Interim Standard 856 (IS-856), Global System forMobile communications (GSM), Enhanced Data rates for GSM Evolution(EDGE), GSM EDGE (GERAN), and the like.

The base station 114 b in FIG. 1A may be a wireless router, Home Node B,Home eNode B, or access point, for example, and may utilize any suitableRAT for facilitating wireless connectivity in a localized area, such asa place of business, a home, a vehicle, a campus, and the like. In oneembodiment, the base station 114 b and the WTRUs 102 c, 102 d mayimplement a radio technology such as IEEE 802.11 to establish a wirelesslocal area network (WLAN). In another embodiment, the base station 114 band the WTRUs 102 c, 102 d may implement a radio technology such as IEEE802.15 to establish a wireless personal area network (WPAN). In yetanother embodiment, the base station 114 b and the WTRUs 102 c, 102 dmay utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE,LTE-A, etc.) to establish a picocell or femtocell. As shown in FIG. 1A,the base station 114 b may have a direct connection to the Internet 110.Thus, the base station 114 b may not be required to access the Internet110 via the core network 106.

The RAN 104 may be in communication with the core network 106, which maybe any type of network configured to provide voice, data, applications,and/or voice over internet protocol (VoIP) services to one or more ofthe WTRUs 102 a, 102 b, 102 c, 102 d. For example, the core network 106may provide call control, billing services, mobile location-basedservices, pre-paid calling, Internet connectivity, video distribution,etc., and/or perform high-level security functions, such as userauthentication. Although not shown in FIG. 1A, it should be appreciatedthat the RAN 104 and/or the core network 106 may be in direct orindirect communication with other RANs that employ the same RAT as theRAN 104 or a different RAT. For example, in addition to being connectedto the RAN 104, which may be utilizing an E-UTRA radio technology, thecore network 106 may also be in communication with another RAN (notshown) employing a GSM radio technology.

The core network 106 may also serve as a gateway for the WTRUs 102 a,102 b, 102 c, 102 d to access the PSTN 108, the Internet 110, and/orother networks 112. The PSTN 108 may include circuit-switched telephonenetworks that provide plain old telephone service (POTS). The Internet110 may include a global system of interconnected computer networks anddevices that use common communication protocols, such as thetransmission control protocol (TCP), user datagram protocol (UDP) andthe internet protocol (IP) in the TCP/IP internet protocol suite. Thenetworks 112 may include wired or wireless communications networks ownedand/or operated by other service providers. For example, the networks112 may include another core network connected to one or more RANs,which may employ the same RAT as the RAN 104 or a different RAT.

Some or all of the WTRUs 102 a, 102 b, 102 c, 102 d in thecommunications system 100 may include multi-mode capabilities, i.e., theWTRUs 102 a, 102 b, 102 c, 102 d may include multiple transceivers forcommunicating with different wireless networks over different wirelesslinks. For example, the WTRU 102 c shown in FIG. 1A may be configured tocommunicate with the base station 114 a, which may employ acellular-based radio technology, and with the base station 114 b, whichmay employ an IEEE 802 radio technology.

FIG. 1B depicts an exemplary wireless transmit/receive unit, WTRU 102.WTRU 102 may be used in one or more of the communications systemsdescribed herein. As shown in FIG. 1B, the WTRU 102 may include aprocessor 118, a transceiver 120, a transmit/receive element 122, aspeaker/microphone 124, a keypad 126, a display/touchpad 128,non-removable memory 130, removable memory 132, a power source 134, aglobal positioning system (GPS) chipset 136, and other peripherals 138.It should be appreciated that the WTRU 102 may include anysub-combination of the foregoing elements while remaining consistentwith an embodiment.

The processor 118 may be a general purpose processor, a special purposeprocessor, a conventional processor, a digital signal processor (DSP), aplurality of microprocessors, one or more microprocessors in associationwith a DSP core, a controller, a microcontroller, Application SpecificIntegrated Circuits (ASICs), Field Programmable Gate Array (FPGAs)circuits, any other type of integrated circuit (IC), a state machine,and the like. The processor 118 may perform signal coding, dataprocessing, power control, input/output processing, and/or any otherfunctionality that enables the WTRU 102 to operate in a wirelessenvironment. The processor 118 may be coupled to the transceiver 120,which may be coupled to the transmit/receive element 122. While FIG. 1Bdepicts the processor 118 and the transceiver 120 as separatecomponents, it should be appreciated that the processor 118 and thetransceiver 120 may be integrated together in an electronic package orchip.

The transmit/receive element 122 may be configured to transmit signalsto, or receive signals from, a base station (e.g., the base station 114a) over the air interface 116. For example, in one embodiment, thetransmit/receive element 122 may be an antenna configured to transmitand/or receive RF signals. In another embodiment, the transmit/receiveelement 122 may be an emitter/detector configured to transmit and/orreceive IR, UV, or visible light signals, for example. In yet anotherembodiment, the transmit/receive element 122 may be configured totransmit and receive both RF and light signals. It should be appreciatedthat the transmit/receive element 122 may be configured to transmitand/or receive any combination of wireless signals.

In addition, although the transmit/receive element 122 is depicted inFIG. 1B as a single element, the WTRU 102 may include any number oftransmit/receive elements 122. More specifically, the WTRU 102 mayemploy MIMO technology. Thus, in one embodiment, the WTRU 102 mayinclude two or more transmit/receive elements 122 (e.g., multipleantennas) for transmitting and receiving wireless signals over the airinterface 116.

The transceiver 120 may be configured to modulate the signals that areto be transmitted by the transmit/receive element 122 and to demodulatethe signals that are received by the transmit/receive element 122. Asnoted above, the WTRU 102 may have multi-mode capabilities. Thus, thetransceiver 120 may include multiple transceivers for enabling the WTRU102 to communicate via multiple RATs, such as UTRA and IEEE 802.11, forexample.

The processor 118 of the WTRU 102 may be coupled to, and may receiveuser input data from, the speaker/microphone 124, the keypad 126, and/orthe display/touchpad 128 (e.g., a liquid crystal display (LCD) displayunit or organic light-emitting diode (OLED) display unit). The processor118 may also output user data to the speaker/microphone 124, the keypad126, and/or the display/touchpad 128. In addition, the processor 118 mayaccess information from, and store data in, any type of suitable memory,such as the non-removable memory 130 and/or the removable memory 132.The non-removable memory 130 may include random-access memory (RAM),read-only memory (ROM), a hard disk, or any other type of memory storagedevice. The removable memory 132 may include a subscriber identitymodule (SIM) card, a memory stick, a secure digital (SD) memory card,and the like. In other embodiments, the processor 118 may accessinformation from, and store data in, memory that is not physicallylocated on the WTRU 102, such as on a server or a home computer (notshown).

The processor 118 may receive power from the power source 134, and maybe configured to distribute and/or control the power to the othercomponents in the WTRU 102. The power source 134 may be any suitabledevice for powering the WTRU 102. For example, the power source 134 mayinclude one or more dry cell batteries (e.g., nickel-cadmium (NiCd),nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion),etc.), solar cells, fuel cells, and the like.

The processor 118 may also be coupled to the GPS chipset 136, which maybe configured to provide location information (e.g., longitude andlatitude) regarding the current location of the WTRU 102. In additionto, or in lieu of, the information from the GPS chipset 136, the WTRU102 may receive location information over the air interface 116 from abase station (e.g., base stations 114 a, 114 b) and/or determine itslocation based on the timing of the signals being received from two ormore nearby base stations. It should be appreciated that the WTRU 102may acquire location information by way of any suitablelocation-determination method while remaining consistent with anembodiment.

The processor 118 may further be coupled to other peripherals 138, whichmay include one or more software and/or hardware modules that provideadditional features, functionality and/or wired or wirelessconnectivity. For example, the peripherals 138 may include anaccelerometer, an e-compass, a satellite transceiver, a digital camera(for photographs or video), a universal serial bus (USB) port, avibration device, a television transceiver, a hands free headset, aBluetooth® module, a frequency modulated (FM) radio unit, a digitalmusic player, a media player, a video game player module, an Internetbrowser, and the like.

FIG. 1C depicts exemplary WLAN devices, one or more of which may be usedto implement one or more of the features described herein, operating ina WLAN system 150. The WLAN system 150 may be configured to implementone or more protocols of the IEEE 802.11 communication standard, whichmay include a channel access scheme, such as DSSS, OFDM, OFDMA, etc. AWLAN may operate in a mode, e.g., an infrastructure mode, an ad-hocmode, etc.

The WLAN system 150 may include, but is not limited to, an access point(AP) 152, a station (STA) 154, and STA 156. The STA 154 and STA 156 maybe associated with the AP 152. A WLAN operating in an infrastructuremode may comprise one or more APs communicating with one or moreassociated STAs. An AP and STA(s) associated with the AP may comprise abasic service set (BSS). For example, AP 152, STA 154, and STA 156 maycomprise BSS 160. An extended service set (ESS) may comprise one or moreAPs (with one or more BSSs) and STA(s) associated with the APs.

An AP may have access to, and/or interface to, a distribution system(DS), which may be wired and/or wireless and may carry traffic to and/orfrom the AP. Traffic to a STA in the WLAN originating from outside theWLAN may be received at an AP in the WLAN, which may send the traffic tothe STA in the WLAN. Traffic originating from a STA in the WLAN to adestination outside the WLAN may be sent to an AP in the WLAN, which maysend the traffic to the destination.

As depicted, the AP 152 is in communication with a network 170. Thenetwork 170 is in communication with a server 180. Traffic between STAswithin the WLAN may be sent through one or more APs. For example, asource STA (e.g., STA 156) may have traffic intended for a destinationSTA (e.g., STA 154). STA 156 may send the traffic to AP 152, and, AP 152may send the traffic to STA 154.

A WLAN may operate in an ad-hoc mode. The ad-hoc mode WLAN may bereferred to as independent BSS. In an ad-hoc mode WLAN, the STAs maycommunicate directly with each other (e.g., STA 154 may communicate withSTA 156 without such communication being routed through an AP).

IEEE 802.11 devices (e.g., IEEE 802.11 APs in a BSS) may use beaconframes to announce the existence of a WLAN network. An AP, such as AP152, may transmit a beacon on a channel, e.g., a fixed channel, such asa primary channel. A STA may use a channel, such as the primary channel,to establish a connection with an AP.

STA(s) and/or AP(s) may use a Carrier Sense Multiple Access withCollision Avoidance (CSMA/CA) channel access mechanism. In CSMA/CA, aSTA and/or an AP may sense the primary channel. For example, if a STAhas data to send, the STA may sense the primary channel. If the primarychannel is detected to be busy, the STA may back off. For example, aWLAN or portion thereof may be configured so that one STA may transmitat a given time, e.g., in a given BSS. Channel access may include RTSand/or CTS signaling. For example, an exchange of a request to send(RTS) frame may be transmitted by a sending device and a clear to send(CTS) frame that may be sent by a receiving device. For example, if anAP has data to send to a STA, the AP may send an RTS frame to the STA.If the STA is ready to receive data, the STA may respond with a CTSframe. The CTS frame may include a time value that may alert other STAsto hold off from accessing the medium while the AP initiating the RTSmay transmit its data. On receiving the CTS frame from the STA, the APmay send the data to the STA.

A device may reserve spectrum via a network allocation vector (NAV)field. For example, in an IEEE 802.11 frame, the NAV field may be usedto reserve a channel for a time period. A STA that wants to transmitdata may set the NAV to the time for which it may expect to use thechannel. When a STA sets the NAV, the NAV may be set for an associatedWLAN or subset thereof (e.g., a BSS). Other STAs may count down the NAVto zero. When the counter reaches a value of zero, the NAV functionalitymay indicate to the other STA that the channel is now available.

The devices in a WLAN, such as an AP or STA, may include one or more ofthe following: a processor, a memory, a radio receiver, and/ortransmitter (e.g., which may be combined in a transceiver), one or moreantennas, etc. A processor function may comprise one or more processors.For example, the processor may comprise one or more of: a generalpurpose processor, a special purpose processor (e.g., a basebandprocessor, a MAC processor, etc.), a digital signal processor (DSP),Application Specific Integrated Circuits (ASICs), Field ProgrammableGate Array (FPGAs) circuits, any other type of integrated circuit (IC),a state machine, and the like. The one or more processors may beintegrated or not integrated with each other. The processor (e.g., theone or more processors or a subset thereof) may be integrated with oneor more other functions (e.g., other functions such as memory). Theprocessor may perform signal coding, data processing, power control,input/output processing, modulation, demodulation, and/or any otherfunctionality that may enable the device to operate in a wirelessenvironment, such as the WLAN of FIG. 1C. The processor may beconfigured to execute processor executable code (e.g., instructions)including, for example, software and/or firmware instructions. Forexample, the processer may be configured to execute computer readableinstructions included on one or more of the processor (e.g., a chipsetthat includes memory and a processor) or memory. Execution of theinstructions may cause the device to perform one or more of thefunctions described herein.

A device may include one or more antennas. The device may employmultiple input multiple output (MIMO) techniques. The one or moreantennas may receive a radio signal. The processor may receive the radiosignal, e.g., via the one or more antennas. The one or more antennas maytransmit a radio signal (e.g., based on a signal sent from theprocessor).

The device may have a memory that may include one or more devices forstoring programming and/or data, such as processor executable code orinstructions (e.g., software, firmware, etc.), electronic data,databases, or other digital information. The memory may include one ormore memory units. One or more memory units may be integrated with oneor more other functions (e.g., other functions included in the device,such as the processor). The memory may include a read-only memory (ROM)(e.g., erasable programmable read only memory (EPROM), electricallyerasable programmable read only memory (EEPROM), etc.), random accessmemory (RAM), magnetic disk storage media, optical storage media, flashmemory devices, and/or other non-transitory computer-readable media forstoring information. The memory may be coupled to the processer. Theprocesser may communicate with one or more entities of memory, e.g., viaa system bus, directly, etc.

A WLAN in infrastructure basic service set (BSS) mode may have an accesspoint (AP) for the basic service set and one or more stations (STAs)associated with the AP. The AP may have access or interface to adistribution system (DS) or another type of wired/wireless network thatmay carry traffic in and out of the BSS. Traffic to STAs may originatefrom outside the BSS, may arrive through the AP and may be delivered tothe STAs. The traffic originating from STAs to destinations outside theBSS may be sent to the AP to be delivered to the respectivedestinations. Traffic between STAs within the BSS may be sent throughthe AP where the source STA may sends traffic to the AP and the AP maydeliver the traffic to the destination STA. The traffic between STAswithin a BSS may be peer-to-peer traffic. Such peer-to-peer traffic maybe sent directly between the source and destination STAs, e.g., with adirect link setup (DLS) using an IEEE 802.11e DLS or an IEEE 802.11ztunneled DLS (TDLS). A WLAN using an independent BSS mode may have noAPs, and the STAs may communicate directly with each other. This mode ofcommunication may be an ad-hoc mode.

Using the IEEE 802.11 infrastructure mode of operation, the AP maytransmit a beacon on a fixed channel, usually the primary channel. Thischannel may be 20 MHz wide, and may be the operating channel of the BSS.This channel may also be used by the STAs to establish a connection withthe AP. The channel access in an IEEE 802.11 system may be Carrier SenseMultiple Access with Collision Avoidance (CSMA/CA). In this mode ofoperation, the STAs, including the AP, may sense the primary channel. Ifthe channel is detected to be busy, the STA may back off. One STA maytransmit at any given time in a given BSS.

FIG. 2 illustrates that 802.11n (High Throughput) may support three PPDUformats (Non-HT PPDU, HT-mixed format PPDU, and HT-greenfield formatPPDU). An 802.11n HT-SIG field is illustrated in Table 1:

TABLE 1 Number Field of bits Explanation and coding Modulation andCoding 7 Index into the MCS table. Scheme See NOTE 1. CBW 20/40 1 Set to0 for 20 MHz or 40 MHz upper/lower. Set to 1 for 40 MHz. HT Length 16The number of octets of data in the PSDU in the range of 0 to 65 535.See NOTE 1 and NOTE 2. Smoothing 1 Set to 1 indicates that channelestimate smoothing is recommended. Set to 0 indicates that onlyper-carrier independent (unsmoothed) channel estimate is recommended.See 20.3.11.11.2. Not Sounding 1 Set to 0 indicates that PPDU is asounding PPDU. Set to 1 indicates that the PPDU is not a sounding PPDU.Reserved 1 Set to 1. Aggregation 1 Set to 1 to indicate that the PPDU inthe data portion of the packet contains an A-MPDU; otherwise, set to 0.STBC 2 Set to a nonzero number, to indicate the difference between thenumber of space-time streams (N_(STS)) and the number of spatial streams(N_(SS)) indicated by the MCS. Set to 00 to indicate no STBC (N_(STS) =N_(SS)). See NOTE 1. FEC coding 1 Set to 1 for LDPC. Set to 0 for BCC.Short GI 1 Set to 1 to indicate that the short GI is used after the HTtraining. Set to 0 otherwise. Number of extension 2 Indicates the numberof extension spatial streams (N_(ESS)). spatial streams Set to 0 for noextension spatial streams. Set to 1 for 1 extension spatial streams. Setto 2 for 2 extension spatial streams. Set to 3 for 3 extension spatialstreams. See NOTE 1. CRC 8 CRC of bits 0-23 in HT-SIG₁ and bits 0-9 inHT-SIG₂. See 20.3.9.4.4. The first bit to be transmitted is bit C7 asexplained in 20.3.9.4.4. Tail Bits 6 Used to terminate the trellis ofthe convolution coder. Set to 0. NOTE 1 - Integer fields are transmittedin unsigned binary format, LSB first. NOTE 2 - A value of 0 in the HTLength field indicates a PPDU that does not include a data field, i.e.NDP. NDP transmissions are used for sounding purposes only (see 9.31.2).The packet ends after the last HT-LTF or the HT-SIG.

The IEEE 802.11ah Task Group was established to develop solutions tosupport WiFi systems in the sub 1 GHz (SIG) band. A 802.11ah PHY may berequired to support 1, 2, 4, 8, and 16 MHz bandwidths. Support for 1 and2 MHz bandwidths may be mandatory in 802.11ah STAs.

FIG. 3 illustrates an example of a SIG short format. FIG. 4 illustratesan example of a SIG field in SIG short format.

FIG. 5 illustrates an example of a STG long format PPDU. FIG. 6illustrates an example of a SIG-A field for a single user transmission.FIG. 7 illustrates an example of a SIG-A field for a multi usertransmission. Table 2 gives the SIG-B field for STG long format.

TABLE 2 Bit Allocation (number of bits) Field 2 MHz 4 MHz 8 MHz 16 MHzDescription MCS B0-B3 B0-B3 B0-B3 B0-B3 Per-user MCS in (4) (4) (4) (4)MU-MIMO Reserved  B4-B11  B4-B12  B4-B14  B4-B14 All ones (8) (9) (11) (11)  CRC B12-B19 B13-B20 B15-B22 B15-B22 (8) (8) (8) (8) Tail B20-B25B21-B26 B23-B28 B23-B28 All zeroes (6) (6) (6) (6) Total # bits 26  27 29  29 

SIG 1 MHz transmissions may be mandatory. FIG. 8 illustrates an exampleof a PPDU in SIG M format. FIG. 9 illustrates an example of a SIG fieldin SIG 1M format.

In 802.11ac, a Very High Throughput (VHT) preamble may be defined tocarry required information to operate in either single-user ormulti-user mode. In order to maintain backward compatibility withnon-VHT STAs, specific non-VHT fields (or legacy fields) may be definedso that they can be received by non-VHT STAs (e.g., to be compliant withClause 17 or Clause 19). The non-VHT fields may be followed by VHTfields specific to VHT STAs. FIG. 10 illustrates an example of a VHTmixed format packet of 802.1 ac.

Information that may be required to interpret VHT format packets may becarried by a VHT-SIG-A field. The VHT-SIG-A field may contain the fieldslisted in Table 3. The VHT-SIG-A field may contain VHT-SIG-AM,containing 24 data bits, as shown in Table 3.

TABLE 3 VHT-SIG-A1 B0-B1 BW 2 Set to 0 for 20 MHz, 1 for 40 MHz, 2 for80 MHz, 3 for 160 MHz and 80 + 80 MHz. B2 Reserved 1 Reserved. Set to 1.B3 STBC 1 Set to 1 if all streams have space time block coding and setto 0 otherwise. B4-B9 Group ID 6 In a SU VHT PPDU, if the PPDU carriesMPDU(s) addressed to an AP or to a mesh STA, the Group ID field is setto 0, otherwise it is set to 63. In an NDP PPDU the Group ID is setaccording to 9.30.6 (Transmission of a VHT NDP). For a MU-MIMO PPDU theGroup ID is set as in 22.3.11.3 (Group ID). B10-B21 N_(STS) 12 For MU: 3bits/user with maximum of 4 users (user u uses bits B(10 + 3u)-B(12 +3u), u = 0, 1, 2, 3). Set to 0 for 0 space time streams Set to 1 for 1space time streams Set to 2 for 2 space time streams Set to 3 for 3space time streams Set to 4 for 4 space time streams Values 5-7 arereserved For SU: B10-B12 Set to 0 for 1 space time streams Set to 1 for2 space time streams Set to 2 for 3 space time streams Set to 3 for 4space time streams Set to 4 for 5 space time streams Set to 5 for 6space time streams Set to 6 for 7 space time streams Set to 7 for 8space time streams B13-B21 Partial AID: Set to the value of the TXVECTORparameter PARTIAL_AID. Partial AID provides an abbreviated indication ofthe intended recipient(s) of the frame (see 9.17a (Partial AID in VHTPPDUs)). B22  TXOP_PS_NOT_ALLOWED 1 Set to 0 by VHT AP if it allowsnon-AP VHT STAs in TXOP power save mode to enter Doze state during aTXOP. Set to 1 otherwise. The bit is reserved and set to 1 in VHT PPDUstransmitted by a VHT non-AP STA. B23  Reserved 1 All ones

The VHT-SIG-A field may contain the fields listed in Table 4. TheVHT-SIG-A field may contain VHT-SIG-A2, containing 24 data bits, asshown in Table 4.

TABLE 4 VHT-SIG-A2 B0-B1 Short GI 2 B0: Set to 0 if short guard intervalis not used in the Data field. Set to 1 if short guard interval is usedin the Data field. B1: Set to 1 if short guard interval is used andN_(SYM) mod 10 = 9, otherwise set to 0. N_(SYM) is defined in 22.4.3(TXTIME and PSDU_LENGTH calculation). B2-B3 Coding 2 B2: For SU, B2 isset to 0 for BCC, 1 for LDPC For MU, if the N_(STS) field for user 0 isnon-zero, then B2 indicates the coding used for user 0; set to 0 for BCCand 1 for LDPC. If the N_(STS) field for user 0 is set to 0, then thisfield is reserved and set to 1. B3: Set to 1 if the LDPC PPDU encodingprocess, or at least one LPDC user's PPDU encoding process, results inan extra OFDM symbol (or symbols) as described in 22.3.10.5.2 (LDPCcoding) and 22.3.10.5.3 (Encoding process for MU transmissions). Set to0 otherwise. B4-B7 MCS 4 For SU: MCS index For MU: If the N_(STS) fieldfor user 1 is non-zero, then B4 indicates coding for user 1: set to 0for BCC, 1 for LDPC. If N_(STS) for user 1 is set to 0, then B4 isreserved and set to 1. If the N_(STS) field for user 2 is non-zero, thenB5 indicates coding for user 2: set to 0 for BCC, 1 for LDPC. If N_(STS)for user 2 is set to 0, then B5 is reserved and set to 1. If the N_(STS)field for user 3 is non-zero, then B6 indicates coding for user 3: setto 0 for BCC, 1 for LDPC. If N_(STS) for user 3 is set to 0, then B6 isreserved and set to 1. B7 is reserved and set to 1. B8 Beam formed 1 ForSU: Set to 1 if a beamforming steering matrix is applied to the waveformin an SU transmission as described in 19.3.11.11.2 (Spatial mapping),set to 0 otherwise. For MU: Reserved and set to 1. B9 Reserved 1Reserved and set to 1. B10-B17 CRC 8 CRC calculated as in 19.3.9.4.4(CRC calculation for HT-SIG) with C7 in B10, etc. B18-B23 Tail 6 Used toterminate the trellis of the convolutional decoder. Set to 0.

VHT-SIG-A1 (Table 3) may be transmitted before VHT-SIG-A2 (Table 4). TheVHT-SIG-A symbols may be BCC encoded at rate, R=½, interleaved, mappedto a BPSK Constellation. The short training field (STF), long trainingfield (LTF), and SIG fields may be referred to as an omni-portion of aMU-MIMO preamble.

Information may be carried by a VHT-SIG-B field. The VHT-SIG-B field maybe specific for providing MU-MIMO information to multiple simultaneousSTAs. The VHT-SIG-B field may contain data bits as shown in Table 5.

TABLE 5 MU Allocation (bits) SU Allocation (bits) 80 MHz, 80 MHz, 160Hz, 160 Hz, Field 20 MHz 40 MHz 80 + 80 MHz 20 MHz 40 MHz 80 + 80 MHzDescription Length  B0-B15  B0-B16  B0-B18  B0-B16  B0-B18  B0-B20Length of (16) (17) (19) (17) (19) (21) useful data in PSDU in units of4 octets MCS B16-B19 B17-B20 B19-B22 N/A N/A N/A  (4)  (4)  (4) ReservedN/A N/A N/A B17-B19 B19-B20 B21-B22 All ones  (3)  (2)  (2) Tail B20-B25B21-B26 B23-B28 B20-B25 B21-B26 B23-B28 All zeroes  (6)  (6)  (6)  (6) (6)  (6) Total # 26 27 29 26 27 29 bits

A group ID concept (introduced by 802.11 ac) may be utilized for DLMU-MIMO transmissions to enable an AP address having a group of STAswith a single ID. Group ID is included in the VHT-SIG-A field (Table 4).The AP may use Group ID Management frames to assign a group ID to STAs.Group ID Management frames may be addressed to the individual STAs andcomprise Membership Status Array and User Position Array.

FIG. 11 illustrates an example of a Membership Status Array field.

FIG. 12 illustrates an example of a User Position Array field.

Null Data Packets (NDP) (e.g., introduced by 802.11ah) may carry simplecontrol/management information. NDP Clear-To-Send (CTS) frame, NDPContention-Free End (CF-End) frame, NDP Power-Save Poll (PS Poll) frame,NDP Acknowledgement (ACK) frame, NDP Block Acknowledgement (BA) frame,NDP Beamforming Report Poll frame, NDP Paging frame, and NDP ProbeRequest frame may be defined.

Preamble design and associated procedures for downlink and uplinkmulti-user simultaneous transmission are described below. WiFi systemshave emphasized support for single user transmissions. 802.11ac and802.11ah, may address improved downlink spectral efficiency by includingsupport for Downlink Multi-User MIMO (DL MU-MIMO). Support for Uplink(UL) MU-MIMO simultaneous transmissions may be needed. Current designsfor UL transmissions may (e.g., may only) consider the requirements forUL Single User (SU) MIMO. Systems and methods for use with UL MU-MIMOsimultaneous transmissions may be provided.

PPDU formats which may be understood by both intended and unintendedSTAs, and by both legacy and non-legacy STAs, may be needed. PPDUformats which support time, spatial, and frequency resource allocationdomains for MU-MIMO operation may be needed.

A Signaling field (SIG) may be required to detect and decode a packet.In 802.11ac, the SIG field may have two parts, the VHT-SIG-A (46 bits)and the VHT-SIG-B (29 bits). The VHT-SIG-A may be further sub-dividedinto VHT-SIG-A1 (23 bits) and VHT-SIG-A2 (23 bits). The SIG fields mayprovide an indication of the frame attributes (including, e.g., thechannel width, MCS). The SIG fields may provide an indication of whetherSU-MIMO or MU-MIMO operation is in operation. The VHT-SIG-B field may bespecific for providing MU-MIMO information to multiple simultaneousSTAs. An indication of the STA's Group ID may be (may also be) providedby the SIG field. A SIG field may comprise a non-trivial overhead forconveying control information to the receiver. If the SIG field is notdecoded properly, it may impact the proper reception of the entire PPDU.Incorporation of PHY-based DL MU-MIMO and/or UL MU-MIMO, and associatedsimultaneous transmissions, may necessitate the indication of additionalparameters to the receiver for proper reception. Systems, methods and/ordevices which enable this indication, including the possible design of anew SIG field, may be necessary to enable these modes of operation.Given the overhead of the SIG design in 802.11, reducing this overhead,and enhancement of the detection probability for these mode of operationmay be beneficial.

STF and LTF may be utilized for start of packet detection,time/frequency synchronization, and/or channel estimation. STF/LTF maybe designed to better fit with simultaneous transmissionimplementations. Synchronization and channel estimation requirements forsimultaneous transmission may be different from single usertransmission, and, the STF/LTF may be re-designed.

Group IDs may be within the range [0,63], where 0/63 indicates singleuser transmission. Thus up to 62 multi-user groups may be supported. Agroup may have up to 4 users. With multiple simultaneous transmissionson both the DL and UL, and potentially multiple simultaneoustransmission modes, the available number of group IDs may not besufficient. The Group ID Management frame may be transmitted by the APusing a unicast transmission. The AP assignment of Group IDs may be doneindividually for a STA, one after the other, which may lead toinefficiencies which may adversely impact the network spectralefficiency. If an AP is required to create a new group of STAs, it mayneed to re-assign the STA's Group IDs. This may be done by transmittinga Group ID Management frame to a (e.g., each) user within the groupprior to the beginning of simultaneous transmissions, which may createundesirable inefficiencies and constraints.

Pilot designs for other simultaneous transmissions, which may involverequirements for DL and UL may require the definition of pilot designs.

Multi-user simultaneous transmissions may require extra control framesto convey additional necessary signaling. The overhead of the controlframes may reduce the system efficiency. NDP packets, which may include(e.g., only include) PHY header and no MAC body, may be used to furtherreduce the overhead of the needed control frames and may increase systemefficiency.

A generic PPDU format may be provided. A PPDU may need to include legacySTF, LTF and/or SIG fields, e.g., in order to support multiplesimultaneous transmission modes, and may at the same time supportbackward compatibility with existing IEEE 802.11 specifications.

FIG. 13 illustrates an exemplary PPDU format design. A high efficiencySIG field (e.g., referred to herein as a hewSIG field) may be positionedin the PPDU following the L-SIG field. The L-STF, L-LTF, L-SIG andhewSIG fields may be transmitted and replicated on each 20 MHz channel.The fields may be transmitted utilizing an omni transmission antennamode. For downlink simultaneous transmissions, when multiple antennasare utilized simultaneously at the transmitter, a cyclic shift diversity(CSD) scheme may be utilized. For uplink simultaneous transmissions, CSDmay not may not be utilized.

The transmission of the fields may depend on the backward compatibilitysupported by the system. For example, if backward compatibility withIEEE 802.11a/g is required, the subcarrier format, sequences, and/or CSDparameters (if applied) may relate to those of 802.11ac non-VHT portiontransmissions (e.g., may be identical to that of 802.1 lac non-VHTportion transmissions). For example, the non-VHT portion may include alegacy portion of a preamble frame format (such as, for example, thenon-VHT fields illustrated in FIG. 10). If backward compatibility withIEEE 802.11a/g is not required, and backward compatibility with802.11ac/n is required, the subcarrier format, sequences, and CSDparameters (if applied) may be identical to those of 802.11ac VHTportion transmissions.

The hewSIG field may be transmitted in a way that enables auto-detectionfrom existing legacy mode, HT mixed mode, and/or VHT mode PPDUs. MU modemay be included in the hewSIG field, which may indicate the detailed MUmode utilized in the packet. The MU mode may indicate SU transmissions,MU transmission with frequency division (OFDMA), MU transmission withspatial division (MU-MIMO), and/or MU transmission with time division(MU-TDMA). FIG. 13 illustrates an 8 us hewSIG, however, the hewSIG fieldmay be a different time duration.

Depending on the MU mode signaled in the hewSIG field, the hewSTF, hewLTF, and/or hewSIGB fields may have different variations. A PPDU whichsupports multiple simultaneous transmission modes may be a highefficiency PPDU, which may be referred to as a high efficiency WLAN(HEW) PPDU.

A HEW PPDU may be utilized, e.g., in order to support UL MU-MIMO. FIG.13 illustrates an exemplary HEW PPDU design, where the uplinktransmissions are operated on a 80 MHz channel. Other channel bandwidthsand other numbers of channels may be employed. Each UL MU-MIMO STA maytransmit L-STF, L-LTF, L-SIG and/or hewSIG field with a 20 MHztransmission format, and may be duplicated on each 20 MHz channels.Other channel bandwidths may be supported.

FIG. 14 illustrates an exemplary PPDU design, which may be referred toas Design 1, where the UL MU-MIMO STAs (e.g., all the UL MU-MIMO STAs)may transmit the full sequence of L-STF and L-LTF in the sub-channels(e.g., all the sub-channels). The UL MU-MIMO STAs may transmit the fullsequence of L-STF and L-LTF with Cyclic Shift Diversity (CSD) among theusers. For example, the full sequence may be a complete preamblesequence that includes L-STF and L-LTF for each antenna. A signalingfield, such as, for example SIG may follow. A L-SIG may carry legacy PHYlayer signaling and may be the same among the UL STAs. The cyclic shiftvalues among multiple users may be different for different types ofchannels. For the case that one UL MU-MIMO STA has more than oneantenna, the transmissions from that STA through multiple antennas mayutilize the CSD scheme and associated parameters defined for single usercase. The UL MU-MIMO STAs may transmit the full sequence of L-STF andL-LTF without Cyclic Shift Diversity (CSD) among the users. The hewSIGfield may be transmitted using the same set of CSD values that areutilized for L-STF and L-LTF. The hewSIG field may be the same amongsome (e.g., all) the UL STAs, which may comprise common information forthis UL MU-MIMO transmission.

The transmitted legacy fields may not be spatially separable, but asthey may be identical, they may be seen by a receiver as multipathreplicas of the same signal. The HEW based fields may be spatiallyseparable (for example, using the P-matrix on the hewLTF) to enable thereceiver to decode the hew SIGB and subsequent data.

FIG. 15 illustrates an exemplary PPDU design, which may be referred toas Design 2, where a user (e.g., only one user) may transmit L-STF,L-LTF, L-SIG, and/or the hewSIG field. The user may be the first userdefined by the UL MU-MIMO group, or the AP may assign one user totransmit, such as by using a control frame prior to the UL MU-MIMOtransmission. The legacy signals may be spatially separate bytransmitting them from a single STA.

The transmission of L-STF, L-LTF, L-SIG and the hewSIG field may besub-divided in the frequency domain. For example, if N users aretransmitting with UL MU-MIMO, user 1 may transmit on sub-carrier index{K, K+N, K+2N, . . . }, while user N may transmit on sub-carrier index{K+N−1, K+2N−1, K+3N−1, . . . }.

The hewSTF/hewLTF fields may be used for multi-user synchronizationand/or channel estimation. The hewSTF/hewLTF fields may be transmittedin a manner that enables the receiver (AP) to distinguish them.

FIG. 16 shows an exemplary hewSTF/hewLTF design for UL MU-MIMO. Forexample, 4 users may transmit simultaneously to the AP using UL MU-MIMO.After transmitting the legacy LTF/STF/SIG and hewSIG fields, each STAmay transmit its hewSTF field. The transmitted hewSTF field duration,e.g., the number of OFDM symbols N_stf, depends on the number of ULMU-MIMO users N_user, and number of data stream for each user, N_sts.

${N\_ stf} = {\sum\limits_{n = 1}^{N\;\_\;{user}}{{N\_ sts}(n)}}$

In the example of 4 users, each user may have one data stream, and theremay be four OFDM symbols utilized for the hewSTF field. Each user mayutilize one OFDM symbol to transmit its own hewSTF. user1/STA1 maytransmit its hewSTF in the first OFDM symbol, where user2/STA2 maytransmit its hew STF in the second OFDM symbol, and so on. The order ofhewSTF transmission may be implicitly signaled in group ID by positionfield. The order of hewSTF transmission may be explicitly by other groupID mechanisms.

In the exemplary design, the hewLTFs may be transmitted using N_ltf OFDMsymbols, where N_ltf is a function of number of UL MU-MIMO users,N_user, and number of data stream for each user, N_sts.

${N\_ ltf} = {\sum\limits_{n = 1}^{N\;\_\;{user}}{{N\_ sts}(n)}}$

In the example of 4 users, each user may have one data stream, and theremay be four OFDM symbols utilized as hewLTF field. User1/STA1 maytransmit its hewLTF in the first OFDM symbol, where user2/STA2 maytransmit its hew STF in the second OFDM symbol, and so on.

FIG. 17 illustrates a hewSTF/hewLTF design for UL MU-MIMO. Users maytransmit hewLTF signals on the OFDM symbols (e.g., all the OFDMsymbols), but may modify the LTF transmission, e.g., using a P-matrix toorthogonalize the transmissions. Overlapping STFs may be used with thereceiver viewing the transmission from the multiple STAs as multipatharrivals of the STF signal.

FIG. 18 describes a design of the hewLTF. In this design, hewSTF mayremain the same as above. The number of OFDM symbols that are used totransmit the hewLTF may be the same or fixed to 1, 2, 4, 6, 8 OFDMsymbols. Scenarios that involve the transmission of a number of datastreams not equal to one of these numbers, may use the next highestnumber (for example, in the case of 3/5/7 data streams from the users,4/6/8 OFDM symbols are utilized for hewLTF respectively).

In an example with 4 users and 1 data stream, for each user there may be4 OFDM symbols utilized for the hewLTF transmission. Different users mayoccupy different frequency domain subcarriers. As an example, in FIG.18, the frequency domain channel may be partitioned to 8 sub-channels.The following allocation may be used: User1/STA1 transmits hewLTF onsub-channel 1 and 5; User2/STA2 transmits hewLTF on sub-channel 2 and 6;User3/STA3 transmits hewLTF on sub-channel 3 and 7; and User4/STA4transmits hewLTF on sub-channel 4 and 8.

A channel may be partitioned to 4 sub-channels in a localized way or adistributed way. Each user/STA may transmit (e.g., may only transmit) ahewLTF sequence on one or some sub-channel(s). The hewLTF sequence maybe defined for the entire channel. Each user/STA may follow one or moreof the following to transmit the hewLTF.

The STA may use the predefined hewLTF sequence. The STA may modulate itto the frequency domain.

The STA may check the group ID and may identify its position in thegroup. Based on this information, the STA may apply a frequency domainfiltering function on the modulated hewLTF fields. The frequency domainfiltering function may be defined as follows:

${F^{n}(k)} = \left\{ \begin{matrix}1 & {k \in {{sub\_ channel}(n)}} \\0 & {otherwise}\end{matrix} \right.$

where k is the subcarrier index, n is the data stream index and n=1, . .. , N_ltf. In the case that each user has one data stream, n may be thesame as user index. Sub_channel(n) may be a set of subcarriers which areassigned to n^(th) stream for hewLTF transmission. Sub_channel(n) may bedefined using following examples:

sub_channel(n)=data_index(n:N _(ltf):end)

where data_index is the set of sub-carriers which are used for datatransmission. For example, with 20 MHz transmission:

data_index={−28:−22;−20:−8;−6:−1;1:6;8:20;22:28}

A small number of sub-carriers, e.g., N_sub, may be pre-groupedtogether, and assigned a sub-channel based on the pre-groupedsub-carrier group. In the case that the total number of sub-carriers isnot divisible by N_sub*N_ltf (for example with 20 Mhz transmission), 52data sub-carriers (N_dc=52) are utilized. For example, in a 2sub-carrier pre-group, if N_ltf=4, since 52 is not divisible by 8,(2*4), the last several sub-carriers may not be pre-grouped.

The sub_channel may be redefined as

${{sub\_ channel}(n)} = \left\{ {{{data\_ index}\left( {\left\lbrack {1:N_{sub}} \right\rbrack + {\left( {n - 1} \right) \cdot {N_{sub}:{N_{sub} \cdot {N_{ltf}:{\left\lbrack {1:N_{sub}} \right\rbrack + {\left( {\left\lfloor \frac{N_{dc}}{N_{ltf} \cdot N_{sub}} \right\rfloor - 1} \right) \cdot N_{ltf} \cdot N_{sub}} + {\left( {n - 1} \right)*N_{sub}}}}}}}} \right)};{{data\_ index}\left( {\left\lfloor \frac{N_{dc}}{N_{ltf} \cdot N_{sub}} \right\rfloor \cdot N_{ltf} \cdot {N_{sub}:{N_{ltf}:{end}}}} \right)}} \right\}$

For example, if N_sub=2, N_ltf=4, 20 MHz transmission, then

sub_channel(1)={−28,−27,−19,−18,−11,−10,−2,−1,8,9,16,17,25}

sub_channel(2)={−26,−25,−17,−16,−9,−8,1,2,10,11,18,19,26}

sub_channel(3)={−24,−23,−15,−14,−6,−5,3,4,12,13,20,22,27}

sub_channel(4)={−22,−20,−13,−12,−4,−3,5,6,14,15,23,24,28}

The two sub_channel and data_index designs are examples.

FIG. 19 illustrates a hewSTF/hewLTF design. The hewSTF may be asdescribed above. The hewLTF transmission may have the same number ofhewLTF symbols as described with respect to FIG. 18. The frequencychannel may be partitioned into multiple sub-channels, and each datastream of each STA may utilize one sub-channel. Instead of transmittinghewLTFs on the same sub-channel for the hewLTF symbols, the hewLTF ofeach data stream may be transmitted in a staggered way. Each user/STAmay use one or more of the following to transmit the hewLTF.

The STA may use the predefined hewLTF sequence. and the STA may modulateit to frequency domain.

The STA may check the group ID and may identify its position in thegroup. Based on this information, the STA may apply a frequency domainfiltering function on the modulated hewLTF fields. The frequency domainfiltering function may be defined as follows:

${F^{n}\left( {m,k} \right)} = \left\{ \begin{matrix}1 & {k \in {{sub\_ channel}\left( {m,n} \right)}} \\0 & {otherwise}\end{matrix} \right.$

Where k is the subcarrier index, n is the data stream index and n=1, . .. , N_ltf. In the case that each user has one data stream, n is the sameas user index. m is hewLTF symbol index, m=1, . . . , N_ltfSub_channel(n) is a set of subcarriers which are assigned to n^(th)stream for hewLTF transmission. Sub_channel(m, n) may be defined usingfollowing examples:

sub_channel((m,n)=data_index(m+n:N _(lft):end)

Where data_index is the set of sub-carriers which are used for datatransmission. For example, with 20 MHz transmission:

data_index={−28:−22;−20:−8;−6:−1;1:6;8:20;22:28}

Or, sub_channel and data_index may use the second design discussed asfor FIG. 18.

With the hewSTF/hewLTF exemplary design for UL MU-MIMO (e.g., as forFIG. 19), it may be possible to utilize a localized sub-channelizationfor hewLTF transmission. The sub_channel and may be designed as

${{sub\_ channel}\left( {m,n} \right)} = {{data\_ index}\left( {\left\lbrack {1:\frac{N_{dc}}{N_{ltf}}} \right\rbrack + {\left( {{{mod}\left( {{m + n},N_{ltf}} \right)} - 2} \right) \cdot \frac{N_{dc}}{N_{ltf}}}} \right)}$

For example, if N_sub=2, N_ltf=4, 20 MHz transmission (N_dc=52), then:

sub_channel(1,1)=sub_channel(2,4)=sub_channel(3,3)=sub_channel(4,2)={−28:−22;−20:−15}

sub_channel(1,2)=sub_channel(2,1)=sub_channel(3,4)=sub_channel(4,3)={−14:−8;−6:−1}

sub_channel(1,3)=sub_channel(2,2)=sub_channel(3,1)=sub_channel(4,4)={1:6;8:14}

sub_channel(1,4)=sub_channel(2,3)=sub_channel(3,2)=sub_channel(4,1)={15:20;22:28}

Turning to FIG. 20, an exemplary PPDU design for OFDMA transmissionswith sub-channel size greater or equal to 20 MHz is illustrated. ThisPPDU format may be referred as long OFDMA PPDU. This design considersbackward compatibility to 802.11a/g or supporting beamforming. Theseimplementations may apply to both uplink and downlink OFDMAtransmission. An exemplary OFDMA PPDU design may be as shown in FIG. 16and FIG. 21. The AP may select the OFDMA PPDU frame format(s) based onthe STAs' capability, whether beamforming is supported, and/or whetherthe system is required to be backward compatible to earlierspecifications.

A long OFDMA PPDU frame format may be used when backward compatibilityto 802.11a/g or beamforming support is needed and may include the legacyestimation and signaling (the L-STF, L-LTF and L-SIG). A short OFDMAPPDU frame format may be used when backward compatibility to 802.11n andno beamforming support is needed, and for example may include just thehigh throughput estimation and signaling (HT-STF, HT-LTF and HT-SIG).

FIG. 21 illustrates an exemplary PPDU design for OFDMA transmissionswith sub-channel size grater or equal to 20 MHz. This PPDU format may ashort OFDMA PPDU. This design considers backward compatibility to802.11n and no beamforming supported.

FIG. 22 illustrates an exemplary OFDMA PPDU format selection (e.g.,long/short). One or more of the following may apply.

The AP may check STA capabilities. The STAs may be STAs with which theAP is associated. The AP may check STA capabilities using a beacon (forexample, the AP may not be associated with the STA). A capability of theSTA to support the short OFDMA PPDU may be exchanged through associationor the beacon (for example, carried in an association request frame, anassociation response frame, a probe response frame, a beacon frame,etc.). For example, the AP may check the STAs' capability field, whichmay indicate support for long and/or short OFDMA PPDU preambles. LongOFDMA PPDU may be required for the STAs (e.g., all the STAs) whichsupport OFDMA operations. If a STA (e.g., at least one STA) involved inthe upcoming DL OFDMA transmission does not support the short OFDMAPPDU, then the AP may decide to use the long preamble. If all the STAssupport a short PPDU format, the short preamble may be used.

The AP may check whether the system is required to support a firstgeneration of legacy devices, which may be 802.11a/g, and/or a secondgeneration of legacy devices, which may be 11n/ac. The check maycomprise checking an operator's capabilities. Checking an operator'scapability for the system may comprise determining whether or not an APwill have capabilities which may support legacy devices. Thesecapabilities may determine how the STAs are handled before association.If 11a/g needs to be supported (e.g., for a STA associated with theupcoming DL OFDMA transmission), the AP may select long OFDMA PPDUformat.

The AP may check whether the upcoming OFDMA transmission involves anybeamforming or precoding transmissions. If yes, the AP may select thelong OFDMA PPDU format, otherwise, the AP may select the short OFDMAPPDU format.

In the case of UL OFDMA transmission, the AP may inform the STAs in theOFDMA transmission the PPDU format selected. For a pending ULtransmission, the AP may inform the STAs of the PPDU format that shouldbe used for the UL transmissions.

FIG. 23 shows an exemplary OFDMA PPDU design, e.g., using a sub-channelsize that is less than 20 MHz which may be backward compatible to802.11a/g, and may support beamforming or other precoding transmissions.With this design, the L-STF, L-LTF, L-SIG and/or hewSIG fields may betransmitted over the entire bandwidth.

These fields may be transmitted over the smallest mandatory supportedbandwidth with current 802.11 standard, and repeated over the entirebandwidth. For example, if the AP is operating on 40 MHz channel, andthe smallest mandatory supported bandwidth is 20 MHz, then the abovementioned fields may be transmitted over the 20 Mhz channel, and may berepeated on the second 20 Mhz channel with or without phase rotation. Inthe case of uplink OFDMA, the difference between the time of arrival ofthe transmission from the multiple STAs may be less than a guardinterval (e.g., so that they appear similar to the effect of a multipathchannel on a single signal). In the case of uplink OFDMA, the hewSIG maybe such that it indicates a change to sub-channelized transmission withdetailed signaling information moved to the hewSIGB field.

Following the hewSIG field, a set of dedicated fields may be transmittedover each sub-channel. The set of dedicated fields may include hewSTF,hewLTF, and/or hewSIGB fields. The dedicated fields may be beamformed orprecoded for each user. The hewSIGB field may contain informationdedicated for one user. This design may be referred as a long OFDMA PPDUformat.

FIG. 24 shows an exemplary short OFDMA PPDU format, which has lesspreamble overhead, and, may be backward compatible to 11ac/n users(e.g., only to such users and not previous generation users) and may notsupport beamforming or other pre-coding schemes. This design may be ashort OFDMA PPDU format. The first portion, which may be utilized tosupport backward compatibility to previous specifications, may includeone set of the STF, LTF and SIG field, and this portion may be decodableby legacy devices (e.g., 11ac/n users). With 20 MHz and 40 MHztransmissions, this set may be associated with HT-STF, HT-LTF and HT-SIGdefined in 802.11n (e.g., identical to HT-STF, HT-LTF and HT-SIG definedin 802.11n). With 80 Mhz or above transmission, these fields may betransmitted over the entire bandwidth, and may use VHT-STF, VHT-LTF andVHT-SIGB format. If these fields are transmitted on 20 MHz channel, andrepeated over the entire bandwidth, then HT-STF, HT-LTF and HT-SIGformat may be utilized.

The hewSIG field may be considered as part of the HEW transmission andmay not be decoded by the legacy devices. However, it may be transmittedfollowing the same waveform and subcarrier format as the LTF fieldtransmitted before it. The hewSIG field may comprise common informationfor the upcoming OFDMA transmission for the users. The hewSIGB field mayfollow hewSIG field, and may comprise dedicated information for a OFDMAuser.

FIG. 25 shows a short OFDMA PPDU format. The sub-channel size may begreater or equal to 20 MHz, and may be backward compatible to802.11ac/n, with no support of beamforming. This design is similar tothat shown in FIG. 24, however, the dedicated hewSIGB field may beomitted here and the necessary information may be included in the hewSIGfield. The AP may select long or short format for OFDMA transmissions.The selection may be as shown in FIG. 22.

FIG. 26 exemplary SIG Field transmission design for the hewSIG fieldwhere two OFDM symbols are utilized. Transmission and auto-detection ofthe hewSIG field may be provided. To enable auto-detection of a HEWsignal, the hewSIG may comprise x OFDM symbols, the first symbol may berotated 90 degrees relative to L-SIG, while the second symbol may berotated 90 degrees relative to the first axSIG symbol and the rotationmay continue for x OFDM symbols. This may enable auto-detection of theHEW signal and differentiation from legacy mode, HT mixed mode, and/orVHT mode preambles. If an example where hewSIG field is made up of twoOFDM symbols, FIG. 26 and Table 6 show the transmission of hewSIG field,and how the auto-detection may be carried out.

For example, assuming that the BPSK signal is denoted as +1 and therotated BPSK signal is denoted as −1, see HEW auto-detection for TABLE6.

TABLE 6 Symbol 0 Symbol 1 Symbol 2 802.11a +1 802.11n MF +1 −1 −1802.11ac +1 +1 −1 802.11ax/HEW +1 −1 +1

The hewSIG field may be common for the transmission modes (e.g., all thetransmission modes). The hewSIG field may include a new parameter whichis used to indicate simultaneous transmission mode, or multi-usertransmission mode, MU mode. An exemplary MU mode value is illustrated inTable 7.

TABLE 7 Value Definition 0 Single user transmission 1 MU-MIMO 2 OFDMA 3MU-TimeThe hewSIG field may include one or more of the following subfields: MUmode; Group ID (e.g., Based on MU mode, different sets of group ID maybe utilized. For example, if MU mode indicates OFDMA transmission, thegroup ID may be interpolated); Direction bit (1 bit); Bandwidth (BW)(besides 20 MHz, 40 MHz, 80 MHz, 160 MHz/80+80 MHz, more bandwidth maybe supported. For example, 60 Mhz, 40 MHz+40 MHz. 3 bits); Doppler (1bit. to support traveling pilots); or NDP indication (indicating an NDPpacket (with an NDP packet, the hewSIG field may be redundant as thereis no data to be transmitted)).

The hewSIG Field may have multiple sub-channels. The hewSIG field may betransmitted with the smallest mandatary channel bandwidth, and may berepeated over the entire band if the operation bandwidth is greater thanthe smallest mandatary bandwidth.

If the operation bandwidth is greater than the smallest mandatarybandwidth, more information may be carried on the extra bandwidth. ThehewSIG field may be different from one sub-channel to another (for thispurpose, sub-channel refers to the channel with the smallest mandatorybandwidth). One bit in hewSIG field transmitted via the primarysub-channel may be used to indicate that the hewSIG field of othersub-channels may comprise different information than the primarysub-channel.

The hewSIGB field may be used to carry user dedicated information suchas the MCS, the interleaving method, beamforming or MIMO mode withnumber of space time streams, methods of feedback, etc.

Mechanisms for Group ID may be provided. Super-Group IDs for differentMU modes may be provided. For example, for different MU modes, anduplink/downlink transmissions, the AP may maintain a different group.The AP may maintain separate groups for DL MU-MIMO, UL MU-MIMO, DLOFDMA, UL OFDMA, DL MU-time and UL MU-time. The super-group ID may bemade up of one or more of: a Multi-user mode indicator (3-bits): DLMU-MIMO group, UL MU-MIMO group, DL OFDMA group, UL OFDMA group, DLMU-time group and/or UL MU-time group; or Group ID (6-bits): a re-use ofthe existing 64 bit group ID method in legacy systems. A STA may havethe same group ID, but this may indicate a different group based on thespecific multi-user mode.

A super-group ID may be made up of one or more of: a transmissiondirection bit (1-bit): uplink or downlink; a group type (3-bits):OFDMA/OFDMA based transmission, MU-MIMO based transmission, TDMA basedtransmission; or a Group ID (6-bits): a re-use of the existing 64 bitgroup ID method in legacy systems.

The super-group ID may be made up of one or more of: a multi-user modeindicator (2-bits): MU-MIMO, OFDMA, MU-Time, SU; direction bit (1-bit):DL, UL; or Group ID: a re-use of the existing 64 bit group ID method inlegacy systems.

Group ID broadcast and efficient assignment may be provided. The GroupID management frame assigning uses to a group may be broadcast from theAP, with the group ID and the MAC addresses of the STAs in the new groupattached. A 2-bit field may be used to indicate one or more of thefollowing: New group, which may set up a new group; Add to group, whichmay add a STA(s) to the group while keeping the existing members of thegroup; Remove from group, which may remove a STA(s) from the group whilekeeping the rest of the members in the group; or Temporarily replace,which may temporarily replace a specific member of the group. Theduration may be for the next x transmissions or may be forever. In thiscase, the member to be replaced may be indicated by an index as opposedto using its MAC address. This may enable transmission to a differentSTA in the case that one member of the group does not have any data totransmit. The STAs that are listed may be added or removed from thegroup more efficiently.

For downlink transmission, the AP may reuse the existing pilots format.With MU-MIMO transmission mode, the AP may precode the pilots in thesame way as it precodes the data carriers. With DL OFDMA transmissions,the STA, as a receiver, may use pilots of the entire band (e.g., notonly the pilots in its dedicated sub-channel(s)) to perform phasetracking. With UL MU-MIMO, the pilots may be designed in an orthogonalway, such that the AP may distinguish pilots for each user easily. WithUL OFDMA, designs may accommodate each STA to have enough pilots forphase tracking (particularly when small sub-channel size, such as 10 MHzor 5 MHz, is utilized).

UL OFDMA transmissions may utilize traveling pilots (e.g., the pilotposition is permuted when the OFDM symbol index is varied). Thepermutation function of traveling pilots may remain the same or varyamong multiple sub-channels. The system may use time varying orthogonalpilot patterns in which the pilot position does not change but the pilotsymbols change over time.

The pilot positions may stay static, but the system may allow a (e.g.,each) UL OFDMA user to transmit pilots over the entire bandwidth, butnot limited to its own sub-channel(s). In order for the receiver (theAP) to distinguish the pilots from different users, the pilots may betransmitted in an orthogonal way. A set of orthogonal sequences may bedefined and a user assigned a sequence.

In dense networks, with Overlapping BSSs, the transmissions of pilots inone BSS may adversely affect (may cause interference) in other BSSs.Cross AP pilot designs may be used in which the Pilot position of one APis set to avoid the pilot position of another AP. Modifying the pilotsymbol energy relative to data symbol energy may help mitigate theeffect of inter-AP pilot interference.

NDP designs for MU control frames may be provided. For UL multi-usersimultaneous transmissions, the AP may need to poll multiple stationsand schedule the uplink transmission, thus there may be extra frameexchanges before the real UL MU transmissions. A set of defined NDPframes that may be utilized for MU control frames may be provided.

FIG. 27 shows an exemplary uplink MU channel access. In this example, MUpoll frame, uplink response frame (ULR), and MU schedule frame areintroduced for MU transmissions. NDP frame formats for these frames maybe provided. For example, one or more of the following fields may beadded to the NDP frames: Direction (1-bit) indicating direction of thetransmission; MU-mode (2-bits or 3-bits) indicating the multi-usertransmission type such as DL MU-MIMO group, UL MU-MIMO group, DL OFDMAgroup, UL OFDMA group, DL MU-time group and/or UL MU-time group (if adirection bit is incorporated, a 2-bit MU-mode may be utilized,otherwise, 3-bit MU-mode may be utilized); Group ID (6-bits): field thatindicates the sub-group ID; or NDP type: field that indicates the typeof NDP transmission; NDP MU Poll; NDP MU Response Frame; and NDP MUSchedule Frame.

Although features and elements are described above in particularcombinations, one of ordinary skill in the art will appreciate that eachfeature or element may be used alone or in any combination with theother features and elements. Other than the 802.11 protocols describedherein, the features and elements described herein may be applicable toother wireless systems. Although the features and elements describedherein may have been described for uplink operation, the methods andprocedures may be applied to downlink operation. Although SIFS may havebeen used herein to indicate various inter frame spacing, other interframe spacing, e.g., RIFS or other agreed time interval may be applied.In addition, the methods described herein may be implemented in acomputer program, software, or firmware incorporated in acomputer-readable medium for execution by a computer or processor.Examples of computer-readable media include electronic signals(transmitted over wired or wireless connections) and computer-readablestorage media. Examples of computer-readable storage media include, butare not limited to, a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, optical media such as CD-ROM disks, and digital versatile disks(DVDs). A processor in association with software may be used toimplement a radio frequency transceiver for use in a WTRU, WTRU,terminal, base station, RNC, or any host computer.

What is claimed:
 1. A station (STA) comprising: a receiver configured toreceive a high efficiency (HE) long training field (LTF) of a data unit,wherein a number of symbols of the HE LTF is based on a number ofspace-time streams utilized for the data unit, wherein the HE LTF isreceived on a subset of subcarriers of a 20 megahertz (MHz) channel, a40 MHz channel, or an 80 MHz channel.
 2. The STA of claim 1, wherein thenumber of space-time streams is 3 and the number of symbols of the HELTF is
 4. 3. The STA of claim 1, wherein the STA is a non access point(non-AP) STA, and wherein the HE LTF of the data unit is received onsubcarriers associated with the number of space-time streams.
 4. The STAof claim 1, wherein the HE LTF is received on the 20 MHz channel.
 5. TheSTA of claim 1, wherein the HE LTF is received on the 40 MHz channel. 6.The STA of claim 1, wherein the HE LTF is received on the 80 MHzchannel.
 7. The STA of claim 4, wherein another transmission is made byanother STA, on the 20 MHz channel, simultaneously with the HE LTF.
 8. Amethod performed by a station (STA), the method comprising: transmittinga high efficiency (HE) long training field (LTF) of a data unit, whereina number of symbols of the HE LTF is based on a number of space-timestreams utilized for the data unit, wherein the HE LTF is transmitted ona subset of subcarriers of a 20 megahertz (MHz) channel, a 40 MHzchannel or an 80 MHz channel.
 9. The method of claim 8, wherein thenumber of space-time streams is 3 and the number of symbols of the HELTF is
 4. 10. The method of claim 8, wherein the STA is a non accesspoint (non-AP) STA, and wherein the HE LTF of the data unit istransmitted on subcarriers associated with the number of space-timestreams.
 11. The method of claim 8, wherein the HE LTF is transmitted onthe 20 MHz channel.
 12. The method of claim 8, wherein the HE LTF istransmitted on the 40 MHz channel.
 13. The method of claim 8, whereinthe HE LTF is transmitted on the 80 MHz channel.
 14. The STA of claim11, wherein another transmission is made by another STA, on the 20 MHzchannel, simultaneously with the HE LTF.
 15. An access point (AP)comprising: a receiver configured to receive a high efficiency (HE) longtraining field (LTF) of a data unit, wherein a number of symbols of theHE LTF is based on a number of space-time streams utilized for the dataunit; wherein the HE LTF is received on a subset of subcarriers of a 20megahertz (MHz) channel, a 40 MHz channel or an 80 MHz channel.
 16. TheAP of claim 15, wherein the number of space-time streams is 3 and thenumber of symbols of the HE LTF is
 4. 17. The AP of claim 15, whereinthe HE LTF of the data unit is received on subcarriers associated withthe number of space-time streams.
 18. The AP of claim 15, wherein the HELTF is transmitted on the 20 MHz channel.
 19. The AP of claim 15,wherein the HE LTF is transmitted on the 40 MHz channel.
 20. The AP ofclaim 18, wherein other data is received from another STA, on the 20 MHzchannel, simultaneously with the HE LTF.